Process for generating burnable gas

ABSTRACT

A process is disclosed for generating burnable gas by gasifying water- and ballast-containing organic materials, be it coal or garbage. The drying, low temperature carbonization and gasification steps are carried out separately. The heat taken form cooled gasified gas is supplied to the endothermic drying low temperature in low temperature carbonation stages. The low temperature carbonization gas is burned in a melting chamber furnace with air and/or oxygen or oxygen-rich flue gas and the liquid slag is evacuated, whereas the low temperature carbonization coke is blown into the hot combustion gases that leave the melting reactions which take place and give carbon monoxide and hydrogen reduce the carbon is removed from the gasified gas, supplied to the melting chamber furnace and completely burned. The advantage of the invention is that the ashes may be transformed into an elution-resistant granulated building material, in that a tar-free burnable gas is generated and in that oxygen consumption is strongly reduced in comparison with the fly stream gasification process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a process for generating burnable gas fromwater- and ballast-containing organic materials, such as coal, municipaland industrial sludges, wood and biomasses, municipal and industrialrefuse and waste and waste products, residues and other materials.

The invention can be used in particular for utilizing the energy ofbiomasses and wood from agricultural areas planted cyclically, inparticular recultivated mining areas, and thus for providing for thecarbon-dioxide-neutral conversion of natural fuels into mechanicalenergy and heat energy and for the productive disposal of municipal,commercial, agricultural and industrial refuse, other organic wastes,residues, byproducts and waste products.

2. Description of Related Art

The prior art is characterized by a number of proposals and practicalapplications for utilizing the energy of plants and organic wastes andmunicipal, commercial, industrial and agricultural refuse. A seminar runin November 1981 by the Kernforschungsanlage Jualich GmbH Julich NuclearResearch Establishment! summarized the prior art on the thermalgeneration of gas from biomass, i.e. gasification and degasification,which still today substantially characterizes the prior art (report ofthe Kernforschungsanlage Jualich-JuilConf-46). Accordingly, processesfor combustion, degasification and gasification, alone or incombination, define the prior art with the following aims: production ofcombustion gas as a source of heat energy for steam generation bycombustion,--production of highly caloric solid and liquid fuels, suchas coke, charcoal and liquid, oil-like tars by low-temperaturecarbonization, degasification and gasification,--production of burnablegas by complete gasification, avoiding solid and liquid fuels.

In the gasification processes, the procedure determines whether theliquid and high-molecular low-temperature carbonization products areobtained or are likewise gasified by oxidation.

The oldest type of gasification is fixed-bed gasification, fuel andgasification medium being moved in counter-current to one another. Theseprocesses achieve maximum gasification efficiency with the minimumoxygen consumption. The disadvantage of this type of gasification isthat the fuel moisture and all known liquid low-temperaturecarbonization products are present in the gasification gas. In addition,this type of gasification requires fuel in piece form. Fluidized-bedgasification, known as Winkler gasification, very largely, but notcompletely, eliminated this deficiency of fixed-bed gasification. In thegasification of the bituminous fuels, the necessary freedom from tar,for example, of the gasification gas, as is required for using the gasas a fuel for internal combustion engines, is achieved. Furthermore,because of the higher mean temperature level in the procedure, incomparison with the fixed-bed gasification, the oxygen consumption ismarkedly higher. In addition, the temperature level of the Winklergasification means that the majority of the input carbon is notconverted into burnable gas, but is discharged again in the form ofdust, and is discharged from the process bound to the ash. Thisdeficiency in the gasification technology can be avoided by thehigh-temperature entrained-bed gasification processes, which generallyoperate above the melting point of the ash.

An example of these is DE 41 39 512 A1. In this process, waste materialsare broken down by low-temperature carbonization into low-temperaturecarbonization gas and low-temperature carbonization coke and thusprocessed into a form necessary for gasification in an exothermicentrained-bed gasifier. The conversion to the exothermic entrained-bedgasifier is associated with further increasing oxygen consumption anddecreasing efficiency, although the organic matter of the wastematerials is virtually completely converted into burnable gas. Thereasons for this lie in the high temperature level of these gasificationprocesses, which cause the majority of the heat generated by the fuel tobe converted into physical enthalpy of the burnable gas.

The deficiency in these technical solutions, as also affects DE 41 39512, was of course recognized internationally by those skilled in theart and responded to with novel solution proposals. The most recentprior art coal gasification is characterized in that a part-stream ofthe coal is burnt in a slag-tap furnace to give hot combustion gas whichis used as gasification medium in the continuation of the process.Introducing the second coal part-stream into the hot gasification mediumcreates the preconditions for an endothermic gasification, and thecombustion gas is converted into burnable gas using the Boudard reactionand water gas reaction. This type of gasification is used in practice inJapan in the NEDO Project and in the USA in the WABASH RIVER Project.This type of gasification is not suitable for wood, residues and refuse,since these materials can only be converted with great mechanical outlayinto the dust form necessary for this procedure.

DE 42 09 549 remedies this deficiency, by connecting a pyrolysis stagefor thermal processing of the fuels, in particular waste materials,upstream of the combination part- stream combustion/endothermicentrained-bed gasification. However, this process has the deficiencythat in this case the hot gasification medium is prepared by burning thepyrolysis coke with air and/or oxygen and the low-temperaturecarbonization gas containing olefins, aromatics etc., is used for thereduction.

However, experience of several years of operating gasifying plants inpractice indicates that burnable gases containing olefin and aromaticscannot be converted, at temperatures up to 1500° C. and in anendothermic procedure, into tar-free burnable gas, as required for useas burnable gas for gas turbines and engines. The essential deficiencyof this procedure is, therefore, that, in the course of the necessarygas cooling and processing, aqueous gas condensates are produced whichcannot be released into the environment in this form, so thatconsiderable outlay is required for their treatment.

SUMMARY OF THE INVENTION

The aim of the invention is to propose a process for gasifying organicmaterials, in particular water- and ballast-containing materials, whichprovides the inorganic portion of these materials at a vitrified,elution-resistant product and converts the organic matter of thesematerials to tar-free burnable gas, which can also be processed to givesynthesis gas, with, in comparison with the entrained-bed gasificationof the prior art, lower consumption of oxygen-containing gasificationmedium, and higher gasification efficiency, based on the chemicalenthalpy of the burnable gas produced.

The technical object of the invention to be achieved is to convert aportion of the physical enthalpy, which is necessary to achieve thetemperature level above the melting point of the inorganic portion ofthe materials to be gasified, back into chemical enthalpy in the courseof the process.

According to the invention this is achieved by means of the fact that,under pressures of 1 to 50 bar, in a

first process stage, the ballast-rich organic materials containing theirorganic and water portions are dried by direct or indirect supply ofphysical enthalpy of the gasification gas and are subjected tolow-temperature carbonization at 350° to 500° C., and are thus thermallydecomposed into low-temperature carbonization gas, which contains theliquid hydrocarbons and the steam, and coke, which principally containscarbon, in addition to the inorganic portion,

second process stage, the low-temperature carbonization gas is burntwith air and/or oxygen, oxygen-containing exhaust gases, e.g. from gasturbines or internal combustion engines, at temperatures above themelting temperature of the inorganic portion of the organic materials,preferably at 1200° to 2000° C., with removal of molten inorganicportion, at an excess air number of 0.8 to 1.3, based on the theoreticalair requirement for complete combustion,

in a third process stage, the combustion gas from the second processstage is converted into gasification gas and the gas temperature isdecreased to 800° to 900° C., by blowing low-temperature carbonizationcoke from the first process stage, if appropriate ground to givepulverized fuel, into the combustion gas at 1200° to 2000° C., whichcoke partially reduces the carbon dioxide to carbon monoxide andpartially reduces the steam to hydrogen, with consumption of heat,

fourth process stage, the gasification gas from the third process stage,if appropriate after indirect and/or direct cooling, is processed togive burnable gas, by dedusting it and chemically cleaning it, andfeeding the dust which still contains carbon, which is produced in thecourse of this process, to the combustion of the low-temperaturecarbonization gas in the second process stage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a an outline technical diagram in accordance with the presentinvention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The efficiency of the invention lies in the fact that the inorganicmatter of ballast-containing organic materials is converted into avitrified elution-resistant building material, with decrease of theconsumption of oxygen-containing gasification medium to the level of thefluidized-bed gasification and complete gasification of the organicmatter at a temperature level which corresponds to the Winklergasification and a higher gasification efficiency in comparison with theprior art, measured by the chemical enthalpy of the burnable gas.

Working example

The invention is described with the aid of the outline technologicaldiagram shown in FIG. 1 and subsequent numerical estimation.

The starting material used is a water- and ballast-containing organicmaterial, a refuse-containing biomass of the following composition (inkg/tonne):

    ______________________________________                                        Constituent       Mass                                                        ______________________________________                                        Carbon            250                                                         Hydrogen           25                                                         Oxygen            150                                                         Nitrogen           8                                                          Sulfur             2                                                          Heavy Metals       3                                                          (Pb, Cd, Hg, Cu, Sn)                                                          Ash               100                                                         Iron/nonferrous metal                                                                            30                                                         Glass/minerals    112                                                         Water              320.                                                       ______________________________________                                    

This starting material is comminuted in a shredder (1) to an edge lengthof 20 to 50 mm and introduced via a gastight lock system (2) into anindirectly heated low-temperature carbonization chamber (3), operatingunder atmospheric pressure, in which the starting material ismechanically agitated as necessary. Owing to the indirect heat supply(4), the starting material dries and carbonizes, and in the course ofthis it decomposes at a final temperature of 40° to 500° C. intoapproximately 405 kg of solid, which approximately comprises 40% carbon,whereas the remainder is composed of minerals, glass, iron andnonferrous metals and heavy metals and ash, and 595 kg oflow-temperature carbonization gas, approximately two thirds of whichcomprises steam, and contains all other known liquid and gaseouslow-temperature carbonization products.

The solids from the low-temperature carbonization are separated underlow-temperature carbonization gas in a screen (5) into a coarsefraction, which principally contains minerals, glass and metal scrap,having an edge length greater than 5 mm, and a fine-grain carbon source.The coarse fraction is discharged from the process via gastight locksystems (6) and, if appropriate, is fed through a separator. The carbonsource remains in the system and is fed to a reduction chamber (9) via acontinuous mill (7) and via a pneumatic transport system (8), which usesthe recycled burnable gas as transport medium. The inorganic portion ofthe carbon source is removed in a gas dedusting stage (10) together withthe carbon not consumed in the reduction chamber (9) and is fed togetherwith the low-temperature carbonization gas produced in thelow-temperature carbonization chamber (3) to a slag-tap furnace (11) andis burned there with oxygen above the melting temperatures of theinorganic matter of the carbon source. The liquid slag produced in thecourse of this process is discharged into a water bath (12) and removedfrom the process from there as elution-resistant building materialgranules. The combustion gas which is at 1200° to 2000° C. passes fromthe slag-tap furnace (11) to the reduction chamber (9), where some ofits carbon dioxide and steam chemically reacts endothermically with thecarbon source to give carbon monoxide and steam, which decreases the gastemperature to 800° to 900° C. The carbon-containing dust produced inthe gas dedusting (10) is likewise fed to the slag-tap furnace (11) by apneumatic transport system (13), which uses recycled burnable gas astransport medium. The burnable gas thus generated corresponds incomposition to a burnable gas which is formed at 800° to 900° C. in thegasification of the organic matter of the starting material with oxygenat atmospheric pressure. It is comparable to a gasification gasgenerated by the fluidized-bed gasification process, using anoxygen/steam mixture as gasification medium.

I claim:
 1. A process for generating burnable gas from organic materialscomprising:drying the organic materials by direct or indirect supply ofphysical enthalpy to form dried materials, and subjecting said driedmaterials to low-temperature carbonization at 350° to 500° C., therebyeffecting thermal decomposition into a carbonization gas comprisingliquid hydrocarbons, steam, and coke, wherein said coke comprises carbonand an inorganic portion; burning the carbonization gas with one or moreof air, oxygen and oxygen-containing exhaust gases at temperatures abovethe melting temperature of said inorganic portion to form combustiongas, and removing molten inorganic portions; converting the combustiongas into gasification gas by decreasing the gas temperature to 800° to900° C., and blowing at least a portion of said coke, which hasoptionally been ground to form a pulverized fuel, into the combustiongas at 1200° to 2000° C., whereby said coke at least partially reducescarbon dioxide present to carbon monoxide, at least partially reducessaid steam to hydrogen, and consumes heat; processing the gasificationgas, optionally after indirect and/or direct cooling, by dedusting andchemically cleaning said gasification gas to produce a burnable gas, andfeeding dust containing carbon removed from said gasification gas tosaid burning step.
 2. A process according to claim 1, wherein saidenthalpy in said drying step is provided by enthalpy from saidconverting step and from said processing step.
 3. A process according toclaim 1, wherein said organic materials are selected from the groupconsisting of water-containing or ballast-containing materials.
 4. Aprocess according to claim 3, wherein said water-containing andballast-containing materials are selected from the group consisting ofcoal, sludge, refuse, wood, and biomasses.
 5. A process according toclaim 1, wherein said organic materials have been previously comminuted.6. A process according to claim 1, wherein the drying step is operatedat atmospheric pressure.
 7. A process according to claim 1, whereinsolids in said carbonization gas formed in the drying step are separatedusing a screen.
 8. A process according to claim 1, wherein saidinorganic portion of the drying step is optionally removed by employinga further gas dedusting step.
 9. A process according to claim 1, whereinthe carbonization gas of the burning step is burnt in a slag-tapfurnace.
 10. A process according to claim 1, wherein theoxygen-containing exhaust gases are selected from the group consistingof exhaust gas from gas turbines and exhaust gas from internalcombustion engines.
 11. A process according to claim 1, wherein themelting temperature of the inorganic portion is in the range of 1200° to2000° C.
 12. A process according to claim 1, wherein the process occursat a pressure of 1 to 50 bar.
 13. A process according to claim 1,wherein said enthalpy in said drying step is provided by heat generatedin said process itself.